The common field thistle:
http://en.wikipedia.org/wiki/Cirsium_arvense edible, nutritious and tasty.
I've been using thistles as a grazing food while out and about for awhile now, other than my discovery of the seeds being edible for some reason I've failed to write about them before.
To the best of my knowledge and I am open to correction on this, all thistles in the UK are edible some however are just not worth the time and effort required to make them so.
The Field Thistle or Common Thistle is the most common and wide spread, found in hedgerows, fields, verges, gardens, wasteland and woodlands throughout the British Isles. The whole of the plant is edible, the leaves are really more effort than they're worth and the roots I hear are an acquired taste. The stems however are easy to access, quite tasty and edible raw or cooked with a slight grassy taste and texture not dissimilar to melon.
I don't make a habit of wearing gloves ymmv but I've never let that stop me taking advantage of this wild edible.
Simply run your blade down the side of the stalk to remove the spiky leaves:
If you keep your knife sharp a quick flick of the wrist will remove the top, then you can remove the portion you've cleared ready to peel and eat:
Because this is a creeping weed after the 1st year or two's growth a good root system should have spread giving you access to a good supply of a food source: Down the middle of the photo below is a long strip of thistles along the edge of a crop field.